I've found that in general Tangs are prone to ich. I have a small blue tang that just got over a really bad case of ich. Its been about a month or two, but I tried everything, garlic fresh water dips, and high salinty. Nothing worked. I went to my LFS and bought Marine NO-Ich. Worked like a charm. It recovered within a week and has been doing great ever since. I do feed garlic as a prevenitive. Not so much a cure, although I've seen it cure some small cases of ich. I'd stay away from the powder blue tangs, I've heard and seen that they get ich more than typical.